Congrats on finishing your last exam! You can finally relax!
You’ve finished your final exam for university, well done!
Good job on completing your final test
「最後のテストお疲れ様」は英語で You’ve completed your final test, well done!とか good job on completing your final test になると思います。 Congrats! You’ve completed your final test でもいいと思います。
私だったらこう言います- Congrats on finishing your last exam! You can finally relaxとか You’ve finally finished your last exam! Well done!
You’ve finished your final exam for university, well done! - 大学最後のテストが終わったね!おめでとう!